1. Field of the Invention
The present invention relates to a vibration damping apparatus which is particularly available for a vehicle engine mount to fully absorb vibration propagated from a variety of vibration generating sources.
2. Background information
A typical vehicle engine is provided with a vibration damping apparatus serving as the engine mount between the engine unit and the vehicle body. Any conventional vibration damping apparatus is internally provided with a main liquid chamber and a sub liquid chamber respectively being filled with liquid, which are internally connected to each other via a plurality of restricting passages. Whenever vibration of engine is propagated to the vibration damping apparatus, liquid in both chambers passes through these restricting passages so as to absorb vibration by the effect of transit resistance or liquid column resonance in the liquid-filled restricting passages.
A typical vehicle engine generates a variety of vibrations including shaking vibration which occurs while the vehicle runs at about 70 kilometers per hour of velocity and idling vibration which occurs while the vehicle runs at an extremely slow velocity such as 5 kilometers per hour for example.
Generally, the shaking vibration generates a maximum frequency of 15 Hz, whereas the idling vibration generates 20 through 40 Hz of frequencies, and thus both vibrations are physically different from each other.
On the other hand, any of the conventional vibration-proof apparatuses is functionally effective only in a specific range in which the frequencies of the vibration can be determined in accordance with the area and the length of aperture of each limited passage. In other words, any conventional vibration damping apparatus cannot effectively damp and absorb vibration containing frequencies out of the predetermined range.
To compensate for this, if any adjustment were applied to such a conventional vibration damping apparatus in order to effectively damp the shaking vibration, then, conversely, it cannot effectively damp the idling vibration, and vice versa.